The present invention relates to a pattern formation method and a pattern formation material, and more particularly, it relates to a pattern formation method for forming a resist pattern, for use in forming a semiconductor device or a semiconductor integrated circuit on a semiconductor substrate, by using exposing light of a wavelength not longer than a 180 nm band and a pattern formation material used in the pattern formation method.
Currently, in fabrication of a mass storage semiconductor integrated circuit, such as a 64 Mbit dynamic random access memory (DRAM) and a logic device or a system LSI with a 0.25 xcexcm through 0.15 xcexcm rule, a resist pattern is formed by using a chemically amplified resist material including a polyhydroxystyrene derivative and an acid generator as principal constituents with KrF excimer laser (wavelength: a 248 nm band) used as exposing light.
Moreover, for fabrication of a 256 Mbit DRAM, a 1 Gbit DRAM or a system LSI with a 0.15 xcexcm through 0.13 xcexcm rule, a pattern formation method using, as exposing light, ArF excimer laser (wavelength: a 193 nm band) lasing at a shorter wavelength than the KrF excimer laser is now under development.
The resist material including a polyhydroxystyrene derivative as a principal constituent has high absorbance against light of a wavelength of a 193 nm band because of an aromatic ring included therein. Therefore, exposing light of a wavelength of a 193 nm band cannot uniformly reach the bottom of a resist film, and hence, a pattern cannot be formed in a good shape. Accordingly, the resist material including a polyhydroxystyrene derivative as a principal constituent cannot be used when the ArF excimer laser is used.
Therefore, a chemically amplified resist material including, as a principal constituent, a polyacrylic acid derivative or a polycycloolefin derivative having no aromatic ring is used when the ArF excimer laser is used as the exposing light.
On the other hand, as exposing light for a pattern formation method capable of coping with high resolution, an electron beam (EB) and the like are being examined.
When the EB is used as the exposing light, however, the throughput is disadvantageously low, and hence, the EB is not suitable to mass production. Thus, the EB is not preferred as the exposing light.
Accordingly, in order to form a resist pattern finer than 0.10 xcexcm, it is necessary to use exposing light of a wavelength shorter than that of the ArF excimer laser, such as Xe2 laser (wavelength: a 172 nm band), F2 laser (wavelength: a 157 nm band), Kr2 laser (wavelength: a 146 nm band), ArKr laser (wavelength: a 134 nm band), Ar2 laser (wavelength: a 126 nm band), soft X-rays (wavelength: a 13, 11 or 5 nm band) and hard X-rays (wavelength: not longer than a 1 nm band). In other words, a resist pattern is required to be formed by using exposing light of a wavelength not longer than a 180 nm band.
Therefore, the present inventors have formed resist patterns by conducting pattern exposure using a F2 laser beam (wavelength: a 157 nm band) on resist films formed from conventionally known chemically amplified resist materials respectively including a polyhydroxystyrene derivative represented by Chemical Formula 21, a polyacrylic acid derivative represented by Chemical Formula 22 and a polycycloolefin derivative represented by Chemical Formula 23. 
Now, a method for forming a resist pattern by using any of the aforementioned conventional chemically amplified resist materials and problems arising in the conventional method will be described with reference to FIGS. 2(a) through 2(d).
First, as shown in FIG. 2(a), the aforementioned chemically amplified resist material is applied on a semiconductor substrate 1 by spin coating and the resultant is heated, so as to form a resist film 2 with a thickness of 0.3 xcexcm. Thereafter, as shown in FIG. 2(b), the resist film 2 is irradiated with a F2 laser beam 4 through a mask 3 for pattern exposure. Thus, an acid is generated from the acid generator in an exposed portion 2a of the resist film 2 while no acid is generated in an unexposed portion 2b of the resist film 2.
Next, as shown in FIG. 2(c), the semiconductor substrate 1 is heated with a hot plate 5 at a temperature of, for example, 100xc2x0 C. for 60 seconds.
Then, the resist film 2 is developed with an alkaline developer, thereby forming a resist pattern 6 as shown in FIG. 2(d).
However, as shown in FIG. 2(d), the resist pattern 6 is formed in a defective pattern shape, and there remains much scum (residues) on the semiconductor substrate 1. Such problems occur not only in using the F2 laser beam as the exposing light but also in using any of the other light of a wavelength not longer than a 180 nm band.
Accordingly, a resist pattern cannot be practically formed by irradiating a resist film formed from any of the aforementioned chemically amplified resist materials with light of a wavelength not longer than a 180 nm band.
In consideration of the aforementioned conventional problems, an object of the invention is forming a resist pattern in a good pattern shape by using exposing light of a wavelength not longer than a 180 nm band with minimally producing scum.
The present inventors have studied the cause of the conventional problems occurring in using the conventional chemically amplified resist materials and have found the following:
First, the chemically amplified resist materials have high absorbance against light of a wavelength not longer than a 180 nm band. For example, a resist film with a thickness of 100 nm formed from the chemically amplified resist material including a polyhydroxystyrene derivative has transmittance of 20% at most against a F2 laser beam (wavelength: a 157 nm band).
Therefore, various examination has been made on means for improving the transmittance of a chemically amplified resist material against light of a wavelength not longer than a 180 nm band. As a result, it has been found that a unit represented by Chemical Formula 1 and a unit represented by Chemical Formula 2 improve the transmittance against light of a wavelength not longer than a 180 nm band.
The present invention was devised on the basis of the aforementioned finding, and specifically provides pattern formation materials and methods described below.
The first pattern formation material comprises a base polymer including a first unit represented by Chemical Formula 1 and a second unit represented by Chemical Formula 2; and an acid generator: 
wherein R1 and R3 are the same or different and are a hydrogen atom, a chlorine atom, a fluorine atom, an alkyl group or an alkyl group including a fluorine atom; R2 is an atom or a group that is not released by an acid and is selected from the group consisting of a hydrogen atom, an alkyl group, a cyclic aliphatic group, an aromatic group, a heterocycle, an ester group and an ether group; R4 is a protecting group released by an acid; m is an integer of 0 through 5; and a and b satisfy 0 less than a less than 1, 0 less than b less than 1 and 0 less than a+bxe2x89xa61.
Since the base polymer of the first pattern formation material includes the first unit and the second unit, the transmittance of a resist film against light of a wavelength not longer than a 180 nm band is improved. Also, since hexafluoroisopropyl alcohol is generated when R4 is released from the second unit owing to the function of an acid, the solubility of an exposed portion of the resist film in a developer is improved, and hence, the contrast in the solubility between the exposed portion and an unexposed portion of the resist film is improved. Furthermore, since the second unit has a benzene ring, resistance against dry etching is improved.
In the first pattern formation material, the base polymer can be prepared through radical polymerization of the first unit and the second unit.
In the first pattern formation material, the base polymer can be prepared by obtaining a polymer through radical polymerization of the first unit and a precursor obtained before substituting R4 for the second unit and by allowing R4 to bond to the precursor included in the polymer.
The second pattern formation material comprises a base polymer including a first unit represented by Chemical Formula 1, a second unit represented by Chemical Formula 2 and a third unit represented by Chemical Formula 3; and an acid generator: 
wherein R1, R3 and R5 are the same or different and are a hydrogen atom, a chlorine atom, a fluorine atom, an alkyl group or an alkyl group including a fluorine atom; R2 is an atom or a group that is not released by an acid and is selected from the group consisting of a hydrogen atom, an alkyl group, a cyclic aliphatic group, an aromatic group, a heterocycle, an ester group and an ether group; R4 is a protecting group released by an acid; m is an integer of 0 through 5; n is an integer of 0 through 5; and a, b and c satisfy 0 less than a less than 1, 0 less than b less than 1, 0 less than c less than 1 and 0 less than a+b+cxe2x89xa61.
In the second pattern formation material, since the base polymer includes the first unit, the second unit and the third unit, the transmittance of a resist film against light of a wavelength not longer than a 180 nm band is largely improved. Also, hexafluoroisopropyl alcohol is generated when R4 is released from the second unit owing to the function of an acid, and the third unit has hexafluoroisopropyl alcohol. Therefore, the solubility of an exposed portion of the resist film in a developer is improved, so that the contrast in the solubility between the exposed portion and an unexposed portion of the resist film can be largely improved. In addition, the wettability of the resist film is improved so as to largely improve adhesion between the resist film and a substrate. Furthermore, since the second unit and the third unit respectively have benzene rings, the resistance against dry etching is largely improved.
In the second pattern formation material, the base polymer can be prepared through radical polymerization of the first unit, the second unit and the third unit.
In the second pattern formation material, the base polymer can be prepared by obtaining a polymer through radical polymerization of the first unit and the third unit and by substituting R4 for some of H of OH groups of the third unit included in the polymer.
The third pattern formation material comprises a base polymer including a first unit represented by Chemical Formula 1 and a second unit represented by Chemical Formula 4; and an acid generator: 
wherein R1 is a hydrogen atom, a chlorine atom, a fluorine atom, an alkyl group or an alkyl group including a fluorine atom; R2 is an atom or a group that is not released by an acid and is selected from the group consisting of a hydrogen atom, an alkyl group, a cyclic aliphatic group, an aromatic group, a heterocycle, an ester group and an ether group; R6 is a protecting group released by an acid; p is an integer of 0 through 5; and a and d satisfy 0 less than a less than 1, 0 less than d less than 1 and 0 less than a+dxe2x89xa61.
In the third pattern formation material, since the base polymer includes the first unit and the second unit, the transmittance of a resist film against the light of a wavelength not longer than a 180 nm band is improved. In particular, since the second unit has a norbornene ring, the transmittance of the resist film against the light of a wavelength not longer than a 180 nm band is further improved than in the first pattern formation material. Also, since hexafluoroisopropyl alcohol is generated when R6 is released from the second unit owing to the function of an acid, the solubility of an exposed portion of the resist film in a developer is improved, so that the contrast in the solubility between the exposed portion and an unexposed portion of the resist film can be improved. Furthermore, since the second unit has a norbornene ring, the resistance against dry etching is improved.
In the third pattern formation material, the base polymer can be prepared through radical polymerization of the first unit and the second unit.
In the third pattern formation material, the base polymer can be prepared by obtaining a polymer through radical polymerization of the first unit and a precursor obtained before substituting R6 for the second unit and by allowing R6 to bond to the precursor included in the polymer.
The fourth pattern formation material comprises a base polymer including a first unit represented by Chemical Formula 1, a second unit represented by Chemical Formula 4 and a third unit represented by Chemical Formula 5; and an acid generator: 
wherein R1 is a hydrogen atom, a chlorine atom, a fluorine atom, an alkyl group or an alkyl group including a fluorine atom; R2 is an atom or a group that is not released by an acid and is selected from the group consisting of a hydrogen atom, an alkyl group, a cyclic aliphatic group, an aromatic group, a heterocycle, an ester group and an ether group; R6 is a protecting group released by an acid; p is an integer of 0 through 5; q is an integer of 0 through 5; and a, d and e satisfy 0 less than a less than 1, 0 less than d less than 1, 0 less than e less than 1 and 0 less than a+d+exe2x89xa61.
In the fourth pattern formation material, since the base polymer includes the first unit, the second unit and the third unit, the transmittance of a resist film against the light of a wavelength not longer than a 180 nm band is largely improved. In particular, since the second unit and the third unit respectively have norbornene rings, the transmittance of the resist film against the light of a wavelength not longer than a 180 nm band is further improved than in the second pattern formation material. Also, since hexafluoroisopropyl alcohol is generated when R6 is released from the second unit owing to the function of an acid and the third unit has hexafluoroisopropyl alcohol, the solubility of an exposed portion of the resist film in a developer is improved so that the contrast in the solubility between the exposed portion and an unexposed portion of the resist film can be largely improved. In addition, the wettability of the resist film is improved so as to largely improve the adhesion between the resist film and a substrate. Furthermore, the second unit and the third unit respectively have norbornene rings, the resistance against dry etching is largely improved.
In the fourth pattern formation material, the base polymer can be prepared through radical polymerization of the first unit, the second unit and the third unit.
In the fourth pattern formation material, the base polymer can be prepared by obtaining a polymer through radical polymerization of the first unit and the third unit and by substituting R6 for some of H of OH groups of the third unit included in the polymer.
The first pattern formation method comprises the steps of forming a resist film by applying, on a substrate, the first pattern formation material; irradiating the resist film with exposing light of a wavelength not longer than a 180 nm band for pattern exposure; and forming a resist pattern by developing the resist film after the pattern exposure.
In the first pattern formation method, since the first pattern formation material is used, the transmittance of the resist film against light of a wavelength not longer than a 180 nm band is improved, the contrast in the solubility between an exposed portion and an unexposed portion of the resist film is improved, and the resistance against dry etching is improved.
The second pattern formation method comprises the steps of forming a resist film by applying, on a substrate, the second pattern formation material; irradiating the resist film with exposing light of a wavelength not longer than a 180 nm band for pattern exposure; and forming a resist pattern by developing the resist film after the pattern exposure.
In the second pattern formation method, since the second pattern formation material is used, the transmittance of the resist film against the light of a wavelength not longer than a 180 nm band is largely improved, the contrast in the solubility between an exposed portion and an unexposed portion of the resist film is largely improved, the adhesion between the resist film and the substrate is largely improved, and the resistance against dry etching is largely improved.
The third pattern formation method comprises the steps of forming a resist film by applying, on a substrate, the third pattern formation material; irradiating the resist film with exposing light of a wavelength not longer than a 180 nm band for pattern exposure; and forming a resist pattern by developing the resist film after the pattern exposure.
In the third pattern formation method, since the third pattern formation material is used, the transmittance of the resist film against the light of a wavelength not longer than a 180 nm band is further improved, the contrast in the solubility between an exposed portion and an unexposed portion of the resist film is improved, and the resistance against dry etching is improved.
The fourth pattern formation method comprises the steps of forming a resist film by applying, on a substrate, the fourth pattern formation material; irradiating the resist film with exposing light of a wavelength not longer than a 180 nm band for pattern exposure; and forming a resist pattern by developing the resist film after the pattern exposure.
In the fourth pattern formation method, since the fourth pattern formation material is used, the transmittance of the resist film against the light of a wavelength not longer than a 180 nm band is more largely improved, the contrast in the solubility between an exposed portion and an unexposed portion of the resist film is largely improved, the adhesion between the resist film and the substrate is largely improved, and the resistance against dry etching is largely improved.
In any of the first through fourth pattern formation methods, the exposing light can be light of a wavelength of a 110 nm through 180 nm band, such as a Xe2 laser beam, a F2 laser beam, a Kr2 laser beam, an ArKr laser beam or an Ar2 laser beam; a soft-X ray beam of a wavelength of a 1 nm through 30 nm band; or a hard-X ray beam of a wavelength not longer than a 1 nm band.